The present invention relates to a stepping motor from which vibration and noise are reduced and to a print device or a paper feed device and a printer using it.
Recently, a stepping motor which outputs a mechanical angle corresponding to an input electrical pulse is extensively used as power for paper feeding, head driving, drum driving or the like of a reproducing machine such as a printer, a scanner, a facsimile machine and the like.
Especially, equipment required having high torque and high accuracy conspicuously uses a hybrid stepping motor in which magnetic flux is formed by a permanent magnet without exciting the motor. That is because such a stepping motor has advantages that it is compact and fast but inexpensively provides power for outputting high torque, does not require a position sensor/encoder and can be controlled easily.
For example, FIG. 29 is a sectional diagram showing a basic structure of a stator and a rotor of a stepping motor. This stepping motor has a stator 2 which has a plurality of stator poles 21 and a rotor 3 which is arranged to oppose these stator poles 21 with a space therebetween. Rotor pole teeth 31 are formed with a given pitch on the rotor 3, and stator pole teeth 22 are formed on each stator pole 21 to oppose the rotor pole teeth 31, so that torque is caused in an output axis 5 by exciting a stator coil 4 disposed on each stator pole 21.
As equipments are being made to operate faster with higher accuracy in recent years, there are disadvantages of vibration and noise caused due to detent torque peculiar to the stepping motor when the motor is running. And, it is an important issue to find a method of reducing the vibration and noise.
To solve the disadvantage, there is conventionally adopted a method of reducing the harmonic contained in the detent torque by setting the pitch of the stator pole teeth to be different from the pitch of the rotor pole teeth.
Generally, it is assumed that the pitch of the rotor pole teeth is PR, the pitch of the stator pole teeth is PS and the number of the stator pole teeth is m, and when they are in the following relation:
PS=PR{1xc2x11/(mxc2x7xcexd)}
it is known that a plurality of harmonics containing the order xcexd are lowered. And, such a structure is adopted to the stepping motor which is disclosed in, for example, Japanese Patent Publication No. Hei 6-14779 and the like.
When the pitch PS of the stator pole teeth is displaced to be made narrow or wide by {PR/(mxc2x7xcexd)} with respect to the pitch PR of the rotor pole teeth, a phase of detent torque caused in each stator pole tooth is displaced appropriately, and specific harmonics cancel each other out.
For example, FIG. 30 is an explanatory diagram showing pitch P1 of the rotor pole teeth 31 and pitch P2 of the stator pole teeth 22 of a conventional stepping motor.
FIG. 30 shows that each stator pole 21 has six stator pole teeth 22, and the pitch PS of the stator pole teeth 22 is set to be narrower (or wider) than the pitch PR of the rotor pole teeth 31 by (PR/18). The harmonics decreased by this structure is not only a third harmonic but also the harmonics of the orders of multiples of three, that is, 6, 9 and 12.
Actually, a three-phase motor was formed by using a stator which has six stator poles and a rotor having 38 rotor pole teeth as shown in FIG. 30. And, its detent torque characteristic was measured. The result shown in FIG. 31 was obtained.
The same measurement was made on a plurality of motors produced experimentally, and the order of the harmonic with respect to detent torque characteristic was analyzed with the frequency, and obtained the results as shown in FIG. 32.
A motor was also produced by using a stator having the same pitch of the stator pole teeth with the pitch of the rotor pole teeth and subjected to the frequency analysis. The results as shown in FIG. 33 and FIG. 34 were obtained.
By comparing the results obtained above, it was confirmed that the sixth harmonic and the 12th harmonic were remarkably decreased when the pitch of the stator pole teeth was determined as shown in FIG. 30.
In the aforesaid drawings, variations in the first and second harmonics seem to result from a dimensional error of the stator and the rotor, eccentricity of the rotation axis or the like.
It is assumed that the nearer the amplitude of the harmonic of each order of the aforesaid stepping motor becomes 0 gcm, the lower the vibration and the noise become.
The harmonics caused in the respective stator poles with different phases are mutually weakened or strengthened, so that the order of detent torque which particularly becomes a problem is decided according to the number of phases and the number of the stator poles.
With the three-phase motor, the fourth harmonic is canceled by the layout of the three-phase structure, and the sixth harmonic becomes a problem. And the aforesaid pitch of the stator pole teeth is set corresponding to such conditions.
In practice, however, it was very hard to achieve satisfactory quietness by the aforesaid structure.
Specifically, when an effect is to be obtained from the layout between the phases and between the stator poles, the accuracy of motor parts manufacturing and assembling processes is extremely restricted, and as a result, a sufficient effect can not be achieved due to a little dimensional error.
It is apparent from FIG. 31 through FIG. 34 that the fourth-order harmonic and the like, which must not constitute a matter of concern as compared with the sixth-order harmonic theoretically, appear largely.
Accordingly, in view of the aforesaid problems, it is an object of the invention to provide a stepping motor which efficiently lowers a harmonic of detent torque and provides quieter and smoother rotations.
As described above, when the stepping motor is driven, its undesired vibration and noise are reduced by lowering or removing detent torque.
The detent torque is torque which retains the rotor in a given position by disposing permanent magnets and the like on the rotor without exciting a stator coil and the like and discriminated from static torque indicated by a so-called stiffness characteristic.
For the stator 2 and the rotor 3 shown in FIG. 29, permanent magnets are arranged in the key points of the rotor 3. The detent torque is present between each stator pole tooth 22 of the stator poles 21 and the rotor pole teeth 31 of the rotor 3 and becomes a total of the detent torque, which exist between the individual pole teeth, as the entire motor. In other words, it is configured that the detent torque caused between the stator pole teeth 22 and the rotor pole teeth 31 which have different phases in the circumferential direction are canceled each other.
The detent torque of one stator pole tooth is represented by a sine wave which has the same cycle with the pitch of the rotor pole teeth. Actually, however, a harmonic component is contained therein, so that it has a complex waveform including distortion as shown in FIG. 35.
Since this harmonic component disturbs the smooth rotations of the rotor, undesired vibration and noise are caused when the motor is running.
Particularly, as disclosed in Japanese Patent Laid-Open Publication No. Hei 9-308213, the stator pole teeth paired mutually are conventionally configured to mutually cancel particular harmonics by properly determining a pitch of the individual pole teeth. But, it was not satisfactory because it was influenced easily by a magnetic imbalance due to eccentricity, falling or the like of the rotor with respect to the stator.
Specifically, the stator pole teeth and the rotor pole teeth usually have a very narrow gap length of tens of xcexcm. Therefore, the aforesaid mutual cancellation becomes incomplete because a difference is caused in the size of the harmonics of both the pole teeth due to eccentricity, falling or the like of the rotor.
And, the reluctance motor pole shape and torque characteristic by Institute of Electrical Engineering (or American Institute of Electrical Engineers), Rotating Machine Research Group, RM-95-55 discloses that when inductance distributions are compared between a case that the rotor has a tooth width narrower than that of the stator and a case that the rotor has a tooth width wider than that of the stator to have the middle between the two inductance distributions, the space distribution of inductance may become very close to the sine wave, so that the rotors having different tooth widths can be stacked. But, since its structure is not apparent, it is hardly put to practical use. Besides, it does not remedy the aforesaid disadvantages resulting from eccentricity, falling or the like of the rotor.
Therefore, in view of the aforesaid problems, it is an object of the invention to provide a stepping motor which can reduce undesired vibration and noise caused by detent torque.
FIG. 36 is a developed diagram showing the arrangement of pole teeth of a conventional two-phase hybrid stepping motor. The stator pole 21 is provided with six pole teeth which have equal pitch 4xcex8s (xcex8s indicates a basic step angle). But, the stepping motor involves vibration and noise because of its operation principle. It is because the stepping motor has detent torque which is periodically produced with respect to a rotation angle of the rotor. Accordingly, technologies have been proposed to improve accuracy of parts which configure the motor and accuracy of assembling such parts in order to reduce the vibration and noise. To decrease the harmonic component of the detent torque, there has been provided an idea of deviating the pitches of the stator pole teeth.
FIG. 37 is a developed diagram showing a positional relation of the pole teeth of a conventional hybrid stepping motor with the pitch of its pole teeth displaced. The pole teeth of the motor shown in FIG. 37 are formed by displacing the positions of the six pole teeth 22 of the stator pole 21 arranged at the equal pitch, i.e., two pole teeth 22c, 22d are not displaced, two pole teeth 22a, 22b are displaced in a forward direction, and two pole teeth 22e, 22f are displaced in a lagging direction. In FIG. 37, the forward direction is rightward.
FIG. 38 is a graph indicating each order component of the torque in this case. FIG. 38 shows a relation between the displacement of the pole teeth and each order component of the torque of the motor with the teeth displaced as shown in FIG. 37. It is assumed that an amount of displacement (mechanical angle) of the pole teeth from the position disposed at the equal pitch is xcex1, a displaced pitch is dt and a basic step angle is xcex8s. Then, they are related as indicated by the following expression (1).
xcex1=dtxc2x74xcex8sxe2x80x83xe2x80x83(1)
The xcexd-th order component T(xcexd) of the torque was obtained by the following expression.       T    ⁡          (      ν      )        =            k      ν        ⁢    ν    ⁢          "LeftBracketingBar"                                    ∑            n                                t            =            1                          ⁢                  sin          ⁡                      (                          ν              ⁡                              (                                                      θ                    m                                    +                                                                                    d                        t                                            ·                      2                                        ⁢                    π                                                  )                                      )                              "RightBracketingBar"      
In the above expression, kxcexd is a coefficient of harmonic of the order xcexd, xcex8m is an electrical angle indicating the position of the pole tooth, and n, which is 6 here, is the number of pole teeth of each stator pole. And, dt is a displaced pitch, and all other various coefficients not relevant to xcexd are determined to be 1 for simplification of the description.
FIG. 38 indicates the following. The harmonic component of torque increases or decreases with dp vibratingly. Therefore, by selecting an appropriate value dp, the harmonic component of torque can be reduced compared with the case that no tooth is displaced. Especially, for the motor as a whole, the component appearing as the detent torque fundamentally is a harmonic component of the order 2PKe (where, P is the number of phases of the stepping motor, and Ke is a positive integer), and other component cancel one another and do not appear. Therefore, when the two-phase motor has dp set to any of 0.063, 0.083, 0.167 and 0.188, the component of the order 4 can be made zero, and the detent torque can be lowered. However, the fundamental harmonic (the order 1) component which becomes main torque decreases with an increase in dp. Therefore, dp is preferably selected to have a value as small as possible. That is, dp=0.063 is suitable to make the fourth order component zero. However, the fundamental harmonic component decreases to 88% even in this case. It is to be noted that nonlinearity of the material is not taken into consideration here.
This phenomenon will be further described with reference to FIG. 39 showing the analytical result with the nonlinearlity of the material taken into account. FIG. 39 shows the result of analyzing the flow of magnetic flux on the stator pole 21a and the rotor pole teeth 31 of the motor by means of a computer. FIG. 39 shows an example of the motor having the pole teeth 22 of the stator pole arranged with a uniform pitch, in which (a) shows that the centers of the pole teeth 31 of the rotor and the pole teeth 22 of the stator are aligned and the pole teeth 31 and 22 are opposed to each other, and (b) shows that the rotor has been turned by a xc2xd pitch from the position of (a), so that the pole teeth 31 and 22 are not opposed to each other. A main torque of the motor is proportional to an effective magnetic flux interlinking with the stator winding in the magnetic flux from the magnets. And the effective magnetic flux is indicated by a difference between the magnetic flux when the pole teeth are mutually opposed as shown in (a) and the magnetic flux when the pole teeth are not opposed as shown in (b). Therefore, the larger the difference of the magnetic flux between (a) and (b) is, the larger the main torque of the motor is.
FIG. 40 shows an example of the motor having the pole teeth displaced as shown in FIG. 37. Similar to FIG. 39, FIG. 40(a) shows that the centers of the pole teeth 31 of the rotor and the pole teeth 22d not displaced of the stator are aligned and the pole teeth 31 and 22d are opposed to each other, and FIG. 40(b) shows that the rotor has been turned by a xc2xd pitch from the position of (a), so that the pole teeth 31 and 22d are not opposed to each other. In FIG. 40, the magnetic flux is hard to flow in (a) while it is easy to flow in (b) by the influence of the pole teeth with their pitch displaced. As a result, the difference of the magnetic flux between (a) and (b) becomes small and lowers to 88% compared with the motor (FIG. 39) which has the pole teeth arranged with an equal pitch. This indicates the reduction of the main torque.
There was a problem of causing the decrease of the main torque when the detent torque was about to be decreased as described above, and an enough torque for practical use could not be obtained.
Accordingly, it is an object of the present invention to provide a hybrid stepping motor by displacing the pitch of any of the plurality of pole teeth formed on the stator pole of a stepping motor to effectively decrease the harmonic component of the detent torque so to suppress the vibration and noise when operating the motor and also the decrease of the fundamental harmonic (first order) component of the torque, thereby enabling to improve the torque performance.
The invention described in claim 1 relates to a stepping motor which comprises a stator having a plurality of stator poles and a rotor disposed to oppose the stator poles with a space therebetween, the rotor having rotor pole teeth disposed with predetermined pitch P1 and the stator poles having stator pole teeth opposed to the rotor pole teeth, wherein:
the stator poles are provided with n sets of tooth groups consisting of the stator pole teeth in the number of m,
pitch P2 of the stator pole teeth in the tooth groups is in the following relation:
P2xe2x89xa0P1,
and pitch P3 of the tooth groups is in the following relations:
P3xe2x89xa0mxc2x7P1
P3xe2x89xa0mxc2x7P2
where, P1, P2 and P3 denote an electrical angle, and m and n are integers of 2 or more.
Thus, the stepping motor according to the present invention is configured to differ the pitch P2 of the stator pole teeth in the group of teeth from the pitch P1 of the rotor pole teeth in order to decrease harmonics and also to decrease the harmonics by the pitch P3 of the group of teeth, thereby decreasing the harmonic of more orders. The idea will be described as follows.
First, the pitch P2 of the stator pole teeth is different from the pitch P1 of the rotor pole teeth in the group of teeth of the stator pole, so that the harmonic of the order corresponding to this difference is decreased.
In addition, one set of tooth groups which consist of the stator pole teeth in number m can be assumed to be one pole tooth corresponding to the rotor pole teeth in number m. Therefore, since the pitch P3 of the tooth group is different from the pitch mxc2x7P1 of the rotor pole teeth in number m, the harmonic of the order corresponding to this difference is decreased, too.
When the pitch P3 of the tooth group is m times the pitch P2 of the stator pole teeth in the tooth group, the pitch of the stator pole teeth becomes constant over the plurality of tooth groups, and the boundary between the tooth group and the tooth group is lost. Therefore, the pitch P3 of the tooth group is made different from the m times the pitch P2 of the stator pole teeth in the tooth group.
Thus, according to the stepping motor of the present invention, the harmonic is decreased efficiently, and quieter and smoother rotation is obtained, because the harmonic of the more orders is decreased in one stator pole.
The invention described in claim 2 relates to the stepping motor according to claim 1, wherein the pitch P2 of the stator pole teeth in the tooth groups is in the following relation,
P2=P1{1xc2x1i/(mxc2x7xcexd)},
and the pitch P3 of the tooth groups is in the following relation,
P3=P1{mxc2x1i/(mxc2x7xcexdxe2x80x2)},
where, xcexd and xcexdxe2x80x2 are the orders of a main harmonic, i is a positive integer which is not a multiple of m, and ixe2x80x2 is a positive integer which is not a multiple of n.
It is generally known that when pitch PR of the rotor pole teeth and pitch PS of the stator pole teeth are in the relation of PS=PR{1xc2x11/(mxc2x7xcexd)}, a plurality of harmonics which contain the order xcexd are decreased.
The harmonics of the individual orders are respectively shown in the sine wave of a given cycle, so that the displacement of such stator pole teeth can be i times (i is a positive integer which is not the multiple of m) the {PR/(mxc2x7xcexd)}.
Therefore, the present invention has summarized the structure based on the above into the structure of claim 1.
That is, the plurality of harmonics which contain the order xcexd are decreased because the pitch P2 of the stator pole teeth in the tooth group is in the relation of P2=P1{1xc2x1i/(mxc2x7xcexd)} with respect to the pitch P1 of the rotor pole teeth.
When the pitch P3 of the tooth group is in the relation of P3=mxc2x7P1{1xc2x1ixe2x80x2/(nxc2x7xcexdxe2x80x2)} with respect to pitch mxc2x7P1 of the rotor pole teeth of the number m, the plurality of harmonics which contain the order xcexdxe2x80x2 are decreased. Here, the displacement of the pitch of the tooth group to the rotor pole teeth of the number m can be (1/m) because the harmonic produced in the tooth group can be decomposed for each of the stator pole teeth of the number m.
Therefore, its expression is indicated as follows:
P3=mxc2x7P1(1xc2x1ixe2x80x2/nxc2x7xcexdxe2x80x2xc2x7m)
P3=P1(mxc2x1ixe2x80x2/nxc2x7xcexdxe2x80x2)
Thus, the plurality of harmonics which contain the orders xcexd and xcexdxe2x80x2 can be decreased by the stepping motor of the present invention.
If the harmonics of the orders 4 and 6 are to be decreased, the pitch P2 of the stator pole teeth in the tooth group and the pitch P3 of the tooth group are set by substituting xcexd=4 and xcexdxe2x80x2=6 or xcexd=6 and xcexdxe2x80x2=4 for the above expressions.
In this case, the values of i and ixe2x80x2 are determined arbitrarily.
The invention described in claim 3 is a stepping motor according to claim 1 or 2, wherein the stepping motor is a three-phase motor which has at least the fourth order harmonic and the sixth order harmonic lowered.
Thus, the stepping motor according to the present invention is, in claim 1 or 2, wherein a three-phase motor which has at least the fourth order and sixth order harmonics decreased, so that the fourth order and sixth order harmonics can be decreased in one stator pole.
Specifically, a particular problem involved in the three-phase motor is conventionally assumed to be the sixth order harmonic, and the pitch of the stator pole teeth is determined according to the aforesaid conditions. In practice, however, in order to obtain the effects by the layouts between the phases and between the stator poles, the accuracy in the motor parts manufacturing and assembling processes was extremely strictly restricted, and it was very difficult to achieve satisfactory quietness. But, the present invention has remedied such disadvantages by decreasing the fourth order and sixth order harmonic in one stator pole.
The invention described in claim 4 relates to a three-phase stepping motor which comprises a stator having a plurality of stator poles and a rotor disposed to oppose the stator poles with a space therebetween, the rotor having rotor pole teeth disposed with a predetermined pitch PR and the stator poles having stator pole teeth opposed to the rotor pole teeth, wherein:
the stator poles are provided with the stator pole teeth in the number of m,
pitch PS of the stator pole teeth is in the following relations:
PS=PR{1xc2x1i/(mxc2x74)},
and
PS=PR{1xc2x1ixe2x80x2/(mxc2x76)},
where, i and ixe2x80x2 are positive integers which are not a multiple of m.
Thus, the stepping motor of the present invention has the fourth order and sixth order harmonics decreased.
Specifically, when the harmonic to be decreased is assumed to be xcexd, it is satisfactory if the following relation is met:
PS=PR{1xc2x1i/(mxc2x7xcexd)},
and a relation that the fourth order harmonic can be decreased is determined by substituting xcexd=4 for the above expression.
When pitch PS of the stator pole teeth calculated from the above relation also has the following relation,
PS=PR{1xc2x1ixe2x80x2/(mxc2x76)}
even the sixth order harmonic can be decreased, so that the relation that the fourth order and sixth order harmonics are decreased is determined by properly setting i and ixe2x80x2.
According to the above expressions, i and ixe2x80x2 are expressed as follows,
i/(mxc2x74)=ixe2x80x2/(mxc2x76)
i/2=ixe2x80x2/3
and can be any values satisfying the above relations.
The invention described in claim 5 relates to a stepping motor which comprises a stator having a plurality of stator poles and a rotor disposed to oppose the stator poles with a space therebetween, the plurality of stator poles being provided with stator pole teeth, and the rotor being provided with rotor pole teeth, wherein the rotor has two rotor cores with different phases of the rotor pole teeth, and the stator and one of the rotor cores as well as the stator and the other rotor core have a plurality of layers with different tooth widths of either or both of the stator pole teeth and the rotor pole teeth in a direction of the rotation axis of the rotor.
Thus, according to the stepping motor of the present invention, the rotor has two rotor cores with different phases of the rotor pole teeth, the stator and one of the rotor cores as well as the stator and the other rotor core have a plurality of layers with different tooth widths of one or both of the stator pole tooth and the rotor pole tooth in the direction of the rotation axis of the rotor, so that waveforms of detent torque produced between one stator pole tooth and the rotor pole tooth of one of the rotor cores as well as between one stator pole tooth and the rotor pole tooth of the other rotor core is approximated to sine wave by combining the detent torques of the respective layers. As a result, these detent torques cancel one another accurately to reduce undesired vibration and noise due to the detent torque.
Especially, harmonics were conventionally cancelled by a pair of stator pole teeth by properly determining a pitch of each pole tooth, but it was not satisfactory because of an influence of magnetic imbalance due to eccentricity, falling or the like of the rotor against the stator. On the other hand, according to the present invention, the waveform of the detent torque is approximated to the sine wave by combining the detent torques of the individual layers, so that an influence of the magnetic imbalance due to the eccentricity, falling or the like of the rotor to the stator is avoided, and an undesired increase of the detent torque is suppressed.
The invention described in claim 6 relates to a stepping motor according to claim 5, wherein the plurality of layers with different tooth widths comprise at least three layers.
Thus, according to the stepping motor of the present invention, a plurality of layers with different tooth widths include at least three layers, so that the detent torque of one stator pole tooth is further approximated to the sine wave.
The invention described in claim 7 relates to a stepping motor according to claim 6, wherein a tooth width ratio of the rotor pole teeth is uniform along a direction of the rotation axis of the rotor, the stator and the rotor cores have a layer of 0.25 to 0.29, a layer of 0.33 to 0.35 and a layer of 0.40 to 0.42 in the average of the tooth width ratio of the stator pole teeth and the tooth width ratio of the rotor pole teeth.
In the stepping motor of the present invention, when the rotor pole teeth have a uniform tooth width ratio along a direction of the rotation axis of the rotor, and the stator and the rotor core have the layer of 0.25 to 0.29, the layer of 0.33 to 0.35 and the layer of 0.40 to 0.42 in the average between the tooth width ratio of the stator pole tooth and the tooth width ratio of the rotor pole tooth, it was experimentally confirmed that a ratio of a harmonic component contained in the detent torque can be made relatively small. Specifically, when the tooth width ratio is determined within the aforesaid ranges, a distortion in the waveform of the detent torque due to the harmonic can be reduced securely.
The invention described in claim 8 relates to a stepping motor according to any of claims 5 through 7, wherein the plurality of layers having the different tooth widths of the stator and the two rotor cores are symmetrically disposed in the direction of the rotation axis of the rotor.
Thus, with the stepping motor of the present invention, the plurality of layers having different tooth widths on the stator and the two rotor cores are symmetrically disposed toward the direction of the rotation axis of the rotor, so that stability of supporting the rotor is secured.
Specifically, when the layers having different tooth widths are laminated, different torque is produced in each layer when the motor is driven, and a balance of supporting the rotor may be degraded. But the present invention can prevent such a situation.
The invention described in claim 9 relates to a stepping motor according to any of claims 1 through 4, wherein at least one pole tooth among the pole teeth of the stator pole is provided with a slanted portion.
The invention described in claim 10 relates to a stepping motor according to any of claims 5 through 8, wherein at least one pole tooth among the pole teeth of the stator pole is displaced to have a different pitch from the other teeth, and a slanted portion is formed on at least one of the displaced pole teeth, by cutting the leading end thereof to have a different shape from the other pole teeth.
Thus, when the shapes of the pole teeth are determined as described above, a fundamental harmonic (first order) component of the torque can be increased by changing easiness of flowing magnetic flux. As a result, the harmonic component of the detent torque can be decreased effectively, vibration and noise during the operation can be suppressed, and lowering of the main torque is suppressed, so that the torque performance can be improved.
Here, when the shapes of the pole teeth are changed, gap permeance changes, but the gap permeance can be kept constant by increasing the tooth width by a level corresponding to the change. But, a width of the dedendum is different between the pole tooth having a different shape and the pole tooth not having a different shape.
Therefore, the invention described in claim 11 relates to a stepping motor according to claim 10, wherein the slanted portion is also formed on the non-displaced pole teeth by cutting off their leading ends so to have the same width at all the dedendums.
Thus, the fundamental harmonic (first order) component of torque can be increased even when the shape of the pole tooth is determined. As a result, vibration and noise during operation can be suppressed, and the torque performance can be improved at the same time.
The invention described in claim 12 relates to a printing device characterized in that the stepping motor according to any of claims 1 through 11 is used as a drive motor for a printhead.
The invention described in claim 13 relates to a paper-feed device, wherein the stepping motor according to any of claims 1 through 11 is used as a drive motor for a paper-feed roller.
The invention described in claim 14 relates to a printer, characterized by using the device according to claim 12 or 13.
The stepping motor of the present invention rotates more quietly and smoothly and its positioning accuracy is also improved. Therefore, it is suitable for office equipment, and particularly for a printing device and a paper-feeding device of a printer.